This invention relates to wrist fixation, and more particularly to an intramedullary rod for internal bridging wrist fixation.
As illustrated in FIG. 1, the wrist joint 10 is formed at the intersection of the radius 15 and the ulna 20 with the metacarpals 25 and the carpals 30. The radius 15 includes an intramedullary canal 33 that runs the length of the radius. The canal 33 has a variable cross-sectional shape and cross-sectional diameter over its length. For example, the canal is wider and more oval shaped near the wrist joint but becomes rounded and narrower in the mid-region of the radius.
The wrist joint 10 and associated bones can be damaged, for example, in a fall. As illustrated in FIGS. 2a-d, a frequent injury to the wrist joint 10 is a distal radius fracture 35 in which a distal portion 40 of the radius is fractured away from the radius. Inherent bony instability, soft tissue damage, and frequent associated injuries make distal radius fractures very difficult to treat. Treatment of the fracture includes placement of a T-plate and external fixation, such as a cast. The functional outcome of the wrist joint after the treatment is generally directly related to residual deformity, both extra-articular alignment and intra-articular step-off, in the joint. FIGS. 2b-d illustrate various types of injuries according to the OTA classification system. For example, FIG. 2b illustrates a Type A injury, which occurs when the fracture line is along the plane of the epiphyseal plate. FIG. 2c illustrates a Type B injury, which occurs when the fracture line is along the margin of the joint. FIG. 2d illustrates a Type C injury, which occurs when the fracture line is along the plane of the epiphyseal plate, but also extends into the joint.
In one general aspect, an intramedullary rod kit for fixation of a distal radius fracture includes an intramedullary rod. The intramedullary rod includes a diaphyseal segment including at least one first mounting section configured to receive a tensioning device, a middle segment, and a joint segment including at least one second mounting section configured to receive a tine. The diaphyseal segment, the middle segment, and the joint segment define a curved configuration that is substantially similar to a curvature of the intramedullary canal of a human radius.
Implementation and embodiments of the intramedullary rod kit may include one or more of the following features. For example, the joint segment may include an opening into a longitudinal channel that extends along a portion of a length of the intramedullary rod. The longitudinal channel may include a threaded portion. The kit may further include a guide that is configured to be mounted to the intramedullary rod and configured to orient drill guides to be collinear with the first mounting section and the second mounting section of the intramedullary rod. The guide may be mounted to the intramedullary rod by insertion of a portion of the guide into the longitudinal channel in the intramedullary rod. The portion of the guide that is inserted into the longitudinal channel may be threadably inserted into the longitudinal channel.
An outer diameter of the intramedullary rod may vary between approximately 10 mm and 25 mm at the joint segment and approximately 2 mm and 9 mm at the diaphyseal segment. More particularly, the outer diameter of the intramedullary rod may vary between approximately 12 mm and 15 mm at the joint segment and approximately 3 mm and 5 mm at the diaphyseal segment. Even more particularly, the outer diameter of the intramedullary rod may vary between approximately 14 mm at the joint segment and approximately 3 mm at the diaphyseal segment.
The joint segment may have one of a round cross-section and an oval cross-section. The diaphyseal segment may have a round or a generally round cross-section. A length of the rod may be between approximately 50 mm and 100 mm, and more particularly, may be approximately 80 mm.
The first mounting section may include at least one channel having a threaded inner diameter and may further include at least one bone screw configured to be passed through the first mounting section to mount the intramedullary rod to a diaphyseal portion of the radius. The bone screw may be one of a unicortical bone screw and a bicortical bone screw.
The tine(s) may include a shaft and may be mounted to the rod in the second mounting section. The second mounting section may include a channel that includes a threaded portion and the tine may include a first non-threaded section and a second threaded section that is configured to be threadably mated to the threaded portion of the channel. The second channel may include a threaded portion and the tine may include a first threaded section and a second threaded section that is configured to be threadably mated to the threaded portion of the channel. The first threaded section may include threads that are configured to be threadably mated with the bone fragment or fragments.
The tine may include an insert from which at least one shaft extends and the insert may be configured to be mated to the second mounting section. The shaft may be integrally formed with the insert. The insert may include a channel that receives a screw and the intramedullary rod may include a threaded channel that also receives the screw. The opening in the intramedullary rod may further include an opening extending through the intramedullary rod and being configured to receive the shaft.
The intramedullary rod kit may further include a snap fit tine that includes a head having an opening into which teeth protrude and from which a tine extends, and the second channel mounting section may be configured as a channel around at least a portion of the circumference of the intramedullary rod and from which teeth protrude, and the head may be configured to be mated with the second mounting section.
The intramedullary rod kit may further include a tensiometer mounted to one or more of the intramedullary rod and the tine and being configured to measure a tension exerted against one or both of the intramedullary rod and the tine. The kit then may include a transmitter for transmitting the measured tension and a receiver for receiving and displaying the measured tension. The intramedullary rod kit may further include written instructions for use, an instructional video, and a drill bit configured to drill a hole in bone tissue.
The tensioning device may be a tie band fastener including a tie band, a slidable tab, and a stop. The tensioning device also may be a molly bolt system that includes a head, a nut, and one or more flexible arms extending between the head and the nut.
The intramedullary rod, the tensioning device, and/or the tine may be coated with a therapeutic agent. The diaphyseal segment of the intramedullary rod may have a dimpled surface.
The details of one or more embodiments of the intramedullary rod and the ancillary and accessory articles are set forth in the accompanying drawings and the description below. Other features and advantages of the intramedullary rod and the ancillary and accessory articles will be apparent from the description, the drawings, and the claims.